Safety Bulletins
FREQUENCY CONTROL SYSTEMS
Following on from the Coroner's inquest, the Chairman of the BMFA, Kath Watson, set up a small group of experienced RC model fliers from a broad range of disciplines to review model flying safety with respect to the Coroner's remarks at the inquest.
You were advised in the BMFA News that the most likely, but not absolute, cause of the accident was the simultaneous operation of two transmitters on the frequency of the accident aircraft. In short a "shoot down". This has prompted the investigating authorities to focus on the methods of frequency control systems in use by model fliers throughout the UK and a review by the select committee mentioned.
This is a topic bound to provoke reaction from all RC model fliers and club committees alike, each believing that the system they use is the best for them.
The review committee identified several different frequency control systems, plus a few variations, which are mentioned below. Doubtless there are many more, all in regular use on club sites up and down the country. However, every system we identified has some potential for error within its operating regime. Humans are not infallible when it comes to following systems such as frequency control and most clubs have identified problems associated with the system they are using. The actions they have taken to try and avoid these problems can lead to some strange variations in otherwise simple systems.
What we ask of you and your club committees is that you read our findings below with an open mind and compare these to your own system. You will find that whichever system you use, it is probably governed by the site from which you fly. Some have many merits, but some are wholly unsuitable for the job they are trying to achieve.
Peg off
The most traditional system in use seems to be the "Peg Off" pegboard, and it is certainly the most common and the most favoured judging by the correspondence since the last BMFA News. It is not, however, infallible.
This system requires the user to remove a frequency peg or marker to indicate that the frequency is in use. The psychological effects of the user being in "control" of the peg are very strong and it is generally a very good system. However once the peg is removed no indication is given of whom is using the frequency. Another flaw in this system is the removal of pegs from the flying site by people forgetting to put them back on the board when they leave. This normally results in a duplicate peg being produced and if the original returns, you have two frequency pegs for the same channel.
Peg on
The second most favoured system is the "Peg On" system. This negates the need for a number of frequency pegs to exist and overcomes the problem of pegs disappearing home at the end of the session. The system requires the user to display an indicator on a pegboard to denote that he is using a given frequency. If the system requires the marker to bear the identification of the owner, and this requirement is adhered to, the system can be very good indeed. It is not unusual, however, to see unmarked indicators, spanners, car keys, battery packs etc. hung on the board to denote that a frequency is in use. The psychological aspect of being in control of the frequency is quite diminished using this system and this is an important part in ensuring that any control system works effectively.
Combined
A third system and the committee's preferred one for suitable sites, is a combination of the two described above. If your infrastructure and site allows you to easily use this system you should seriously consider it. Frequency markers exist as with the "Peg Off" system but when they are removed from the board, hook or whatever, they are replaced with an indicator of a distinctly different design bearing the identification of the person using the frequency. The psychological reassurance is back and if a peg does go home with the user they will probably have left their own named marker in its place. A new indicator can be made when it is clear that the original is irrecoverable, and temporary "Missing Peg" indicators can be used if the original is expected back. A simple way to avoid the markers going home is to remove the requirement for them to be displayed on the user's transmitter or placed in his pocket. You may request that they be placed by the users flight box in his personal pit area or even on the flight line, and of course if the frequency is cleared after every flight, which it should be, the marker will be back on the board anyway!
Indicator system
A fourth system, and one in use by many slope soaring clubs is where the user is required to place an indicator in a communal place on the ground or a wire on a fence etc. bearing his name and frequency number to denote that he is using that channel. This has many variations but the principal flaw seems to be that in some instances it does not tell other fliers if that frequency is actually in use at a given time; only that someone on the hill has a transmitter on that channel. There is then the added problem of expecting all fliers to congregate at the same point on the hill, and the issue of trying to determine if a fellow flier has gone off home leaving his peg, or merely go to fly "cross country".
Scanners
We also identified occurrences of clubs using electronic frequency scanners as the primary means of frequency control. This system is fundamentally flawed as it only tells the viewer which frequencies are in use at the time. There is no identification of the user, nor the number of users on the same channel. The use of a scanner is however a very, very good secondary system when used as a cross-check against a more traditional pegboard system. In this instance it can be utilised to check that the frequency pegs out in the field are actually in use.
Transmitter Pound
We cannot rule out the use of a transmitter pound as a possibility for club sites although they can be very labour intensive and would only generally tend to suit clubs with adequate resources to man them correctly. The transmitter pound is almost universally found at model flying displays and is always used in conjunction with a traditional peg board system, typically peg off. It allows some insurance against the simultaneous operations of two transmitters on the same frequency as it employs the use of a third party who is monitoring the frequencies in use and ensuring that only one transmitter on any frequency is out in the field at one time. This third party also ensures that a transmitter is back in his custody before he allows another on that frequency to be taken from the pound.